Sensor-Based Communication Apparatus And Method, And Communication Medium

ABSTRACT

In a described embodiment, a sensor-based communication apparatus (100) is disclosed. The communication apparatus (100) comprises a plurality of sensor nodes (112) associated with respective unique pulse signatures (200) and adapted to communicate with respective sensors (113) with each sensor (113) configured to generate a sensory signal (113a) in response to a respective stimulus (113b). Each sensor node (112) is triggered, upon receipt of the corresponding sensory signal (113a), to transmit the associated unique pulse signature (200) independently and asynchronously through a transmission medium (110) shared by the sensor nodes (112), and the unique pulse signatures (200) transmitted by the sensor nodes (112) being a representation (300) of a stimulus event associated with the stimuli detected by the corresponding sensors (113). A method and a communication medium are also disclosed.

TECHNICAL FIELD

The present disclosure relates to a sensor-based communicationapparatus, a sensor-based communication method, and a communicationmedium.

BACKGROUND

Artificial somatosensory perception typically requires sensor arraysthat can capture and process rapidly varying contact stimuli overnon-uniform surfaces. Electronic skins (e-skins) are electronic devicesthat are arrayed to facilitate the sensing of human-machine-environmentinteractions with applications in advanced collaborative anthropomorphicrobots and neuro-prosthetics. Although much progress has been made indeveloping compliant e-skin sensors with high sensitivity, known signalcommunication arrangements of such e-skin sensors have numerousdisadvantages.

One known arrangement of the sensors relies on conventional TimeDivision Multiple Access (TDMA) architectures for signal communications,in which the sensors are sampled at a predetermined frequency orpredetermined time slots. TDMA based sensor systems are known to havepoor scalability because sequential data acquisition leads to a greatertransmission latency in larger arrays. Further, the conventionalrow-column wiring for addressing individual sensors is prone to damage.In addition, highly localized and transient contact stimuli, such as aneedle prick or an object slip, may be missed if the sensor samplingfrequency is too low.

Another arrangement relies on Code Divisional Multiple Access (CDMA)techniques for wireless signal communications. CDMA is more complex dueto the need for signal modulation from an intermediate frequency to acarrier frequency. Additional modules for power regulation are alsorequired. Moreover, CDMA uses level shifted codes, which are relativelysusceptible to low frequency interferences (e.g., AC power noises).Further, CDMA typically requires expensive high resolution ADCs. CDMA isalso known to have a low capacity.

Another known arrangement involves Address Event Representations (AER).AER relies on asynchronous hand-shakes to time-multiplex data packets ona first-come-first-served basis. AER requires an implementation ofarbitration logic in order to determine which packet to transmit firstin the event of a packet collision, which results in a more complexnetwork.

Optical CDMA is another known signal communication arrangement, known touse unipolar pulses and hence requiring additional synchronizationsignals and protocols. Dedicated electro-optical components are alsorequired.

Yet another arrangement uses Ethernet. It does not support simultaneouspacket transmission from a plurality of nodes. Further, transmissionoverheads (such as Carrier Sense Multiple Access) are needed to preventpacket collision, and multiple, separate conductors are needed toimplement the protocols.

It is desirable to provide a sensor-based communication apparatus, asensor-based communication method, and a communication medium, whichaddress at least one of the drawbacks of the prior art and/or to providethe public with a useful choice.

SUMMARY

According to a first aspect, there is provided a sensor-basedcommunication apparatus comprising: a plurality of sensor nodesassociated with respective unique pulse signatures and adapted tocommunicate with respective sensors with each sensor configured togenerate a sensory signal in response to a respective stimulus, whereineach sensor node is triggered, upon receipt of the corresponding sensorysignal, to transmit the associated unique pulse signature independentlyand asynchronously through a transmission medium shared by the sensornodes, the unique pulse signatures transmitted by the sensor nodes beinga representation of a stimulus event associated with the stimulidetected by the corresponding sensors.

The described embodiment is particularly advantageous. For example,since the sensor nodes are configured to transmit the respective pulsesignatures independently with each trigger, i.e. on receipt of thestimulus, a highly efficient signalling scheme may be achieved. Sincethe described embodiment includes using event-based sensing elementsresponding to a single stimulus event, a resultant pattern in space andtime may be used to represent the stimulus event.

Preferably, each inter-pulse interval of the unique pulse signature ofeach of the sensor nodes may have a unique duration. Such an arrangementis useful in reducing the probability of collision of pulses transmittedby the sensor nodes.

The unique pulse signature may have eight or ten pulses, or any numberof pulses. An optimal performance of Signal to Interference and NoiseRatio (SINR) can be achieved when the number of pulses fall within or isclose to this range or the alternative range of 8 to 14 pulses.

Alternatively, the unique pulse signature of one of the sensor nodes mayhave a first number of pulses and the unique pulse signature of anotherof the sensor nodes may have a second number of pulses different fromthe first number. This arrangement allows the numbers of pulses to beflexibly determined, for example, based on the types and numbers ofassociated sensors.

Preferably, the unique pulse signature has a signature duration of 1 ms(millisecond). This allows the sensor nodes to mimic the transmissionperformance of the biological counterparts. The signature duration mayalso be adjusted to meet various capacity needs.

Alternatively, the unique pulse signature of one of the sensor nodes mayhave a first signature duration and the unique pulse signature ofanother of the sensor nodes may have a second signature durationdifferent from the first signature duration. This arrangement allows thesignature durations to be flexibly determined, for example, based on thetypes and numbers of associated sensors.

Preferably, the unique pulse signature may have a pulse duration of 60ns (nanoseconds). This allows the sensor nodes to mimic the transmissionperformance of the biological counterparts. More preferably, the uniquepulse signature may have a pulse duration shorter than 60 ns(nanoseconds) which may maximise capacity and minimise error rates.

Alternatively, the unique pulse signature of one of the sensor nodes mayhave a first pulse duration and the unique pulse signature of another ofthe sensor nodes may have a second pulse duration different from thefirst pulse duration. This arrangement allows the pulse durations to beflexibly determined, for example, based on the types and numbers ofassociated sensors.

Preferably, the apparatus further comprises the sensors. The apparatusmay be manufactured so that each sensor node is integrated with orotherwise associated with a corresponding sensor. Where the apparatusdoes not comprise the sensors, the sensor nodes of the apparatus may beadapted to be associated with external sensors. The sensors may includetactile sensors of different sensitivities. By mixing sensors ofdifferent sensitivities, a more accurate, comprehensive representationof the stimulus event can be obtained. Further, the sensors may includetemperature sensors. Other types of sensors may also be included such aselectro-magnetic, humidity, surface texture, vibration, accelerationand/or optical sensors etc.

Preferably, each sensor node may be triggered, upon receiving a currentvalue in the corresponding sensory signal, to transmit a current one ofthe associated unique pulse signature to indicate the current value byan interval between the current one of the associated unique pulsesignature and a previous one of the associated unique pulse signature.This arrangement is useful when the sensor node is associated with asensor which generates a sensory signal representing a current value ofdetection by the sensor. For example, the sensory signal may have astate representing the current value. A slow adapting (SA) sensor (or apiezoresistive resistive element configured to be a slow adaptingsensor) is one such sensor.

The sensor nodes may be adapted to be associated with one of a robot, ahuman and a vehicle, or a robot may comprise such a sensor-basedcommunication apparatus.

Preferably, the sensor nodes may harvest power from an external energysource. Such a source may be a source of electromagnetic waves,mechanical motions, solar energy, chemical substances, or the likes.

The apparatus may further comprise: a receiver configured to receivethrough the transmission medium an incoming signal relating to thetransmitted unique pulse signatures, to correlate the associated uniquepulse signature of each sensor node with an intermediate signal relatingto the incoming signal, and to provide indication signals indicatingrespective times of triggering of the sensor nodes based on a result ofcorrelation for representation of the stimulus event. The receiver maybe locally or remotely located with respect to the sensor nodes.

Preferably, the receiver includes a plurality of filters each activated,upon detection of an edge in the incoming signal by the receiver, tocorrelate the intermediate signal with a corresponding one of the uniquepulse signatures. This arrangement allows the filters to be activated tocorrelate the intermediate signal with the signatures in parallel whenthe edge is detected in the incoming signal. That is, the filters mayremain deactivated to save power when no signature is transmitted (thusno edge). Other components (e.g., correlation threshold circuits)associated with the filters may be activated and deactivatedcorrespondingly.

The transmission medium may include a conductive medium, and the sensornodes may be distributed along the conductive medium and electricallycoupled to one another through the conductive medium. Preferably, thesensor nodes are arranged on a surface of the conductive medium.Preferably, the sensor nodes are embedded in the conductive medium.Preferably, the conductive medium is made of polymer. Preferably, theconductive medium is elastic and flexible. Preferably, the conductivemedium is mesh or planar in form. With one or more of such arrangements,signal communication via the conductive medium is resistant to damagessuch as tears. Communication between two portions of the conductivemedium remains unaffected unless one portion is completely torn orotherwise removed from the other portion.

The conductive medium may include at least one of a conductive fabric, aconductive bulk conductor, a conductive substrate, a conductive solid, aconductive gel, and a conductive fluid. For example, when the conductivemedium is implemented in the form of a fabric or substrate may besuitable for electronic skin applications. For the avoidance of doubt,“fluid” can include, but is not limited to, “liquid”.

It is envisaged that each sensor node may be associated with one or moreunique pulse signatures. Preferably, each sensor node may be furtherassociated with a further (or another) unique pulse signature. Thisarrangement is useful when the sensory signal of each sensor has twostates. Each sensor node may be triggered, upon receipt of thecorresponding sensory signal in a first state, to transmit theassociated unique pulse signature, and upon receipt of the correspondingsensory signal in a second state, to transmit the associated furtherunique pulse signature independently through the transmission medium.The unique pulse signatures associated to each sensor node maycorrespond to or exceed the number of states in the correspondingsensory signal.

Each sensor node may be configured to transmit the associated furtherunique pulse signature independently through the transmission medium toindicate an internal state of the respective sensor node. Thisarrangement reduces the need for another communication path or channelfor indicating the internal state.

Further, the unique pulse signatures of each sensor node may havedifferent pulse polarities. For example, two signatures assigned to asensor node may have the same pulse positions and opposite pulsepolarities, where a pulse polarity is a positive or negative voltagepotential. Further, two signatures of a sensor node may be otherwisedifferent, either partially or wholly.

Advantageous, the representation of the stimulus event may be aspatiotemporal representation.

In a second aspect, there is provided a sensor-based communicationmethod comprising: receiving a sensory signal generated by acorresponding sensor in response to a respective stimulus, and uponreceipt of the sensory signal, triggering respective ones of a pluralityof sensor nodes to transmit an associated unique pulse signatureindependently and asynchronously through a transmission medium shared bythe sensor nodes, the unique pulse signatures transmitted by the sensornodes being a representation of a stimulus event associated with thestimuli detected by the corresponding sensors.

In a third aspect, there is provided a communication medium comprising:a conductive medium; and a plurality of sensor nodes distributed alongthe conductive medium and electrically coupled to one another throughthe conductive medium.

The conductive medium of the described embodiment provides a high degreeof flexibility in sensor node placement, and provides robust signalconducting paths for the sensor nodes.

It is envisaged that features relating to one aspect may be applicableto the other aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments will now be described hereinafter with reference tothe accompanying drawings, wherein like parts are denoted by likereference numerals. Among the drawings:

FIG. 1 is a schematic diagram of a sensor-based communication apparatusaccording to an embodiment of the present disclosure;

FIG. 2 is an enlarged partial isometric view of a communication mediumof the apparatus of FIG. 1;

FIG. 3 is a schematic diagram showing some components of each sensornode of the communication medium and a summing circuit of the apparatusof FIG. 1;

FIG. 4 is a schematic diagram showing some components of a receiver ofthe apparatus of FIG. 1;

FIG. 5 is a timing diagram of a unique pulse signature of one of thesensor nodes of the apparatus of FIG. 1;

FIG. 6 is another timing diagram of another unique pulse signature ofanother one of the sensor nodes of the apparatus of FIG. 1, shown nextto the timing diagram of FIG. 5 for comparison;

FIG. 7A comprises FIGS. 7A(i), (ii) and (iii) to compare timing diagramsof an incoming signal received by the receiver of the apparatus of FIG.1 and indication signals accordingly generated by the receiver of theapparatus of FIG. 1 in one scenario;

FIG. 7B is a timing diagram showing a spatiotemporal representation of astimulation event based on pulse signatures transmitted by five sensornodes of the apparatus of FIG. 1 in another scenario;

FIG. 7C shows an incoming signal corresponding to the timing diagram ofFIG. 7B;

FIG. 7D is a timing diagram showing corresponding indication signalsprovided by the receiver of FIG. 1 in the scenario of FIG. 7B;

FIG. 8 shows a series of representations of different time points,illustrating a spatiotemporal representation of a tactile stimulationevent;

FIG. 9A is a timing diagram of another example pulse signature with 14pulses;

FIG. 9B is a diagram of temporal precisions versus numbers ofoverlapping pulse signatures;

FIG. 9C is a diagram showing relationships between correlation thresholdvalues with detection error probabilities;

FIG. 9D shows a diagram of Signal to Interference and Noise Ratio (SINR)of an output of the receiver of FIG. 1 versus the number of overlappingsignatures, obtained in each of a simulation and an experiment;

FIG. 9E shows a diagram of SINR of the output of the receiver of FIG. 1versus the number of overlapping signatures, obtained for differentpulse widths;

FIG. 9F shows a diagram of SINR of the output of the receiver of FIG. 1versus the number of overlapping signatures, obtained for differentnumbers of pulses in each signature;

FIG. 10 shows steps of an example method of an algorithm for generatingpulse signatures for use by the apparatus of FIG. 1;

FIG. 11A is plot of pressures sensed by a fast adapting sensor and aslow adapting sensor in relation to a load cell over time, obtainedusing another embodiment of the apparatus of the present disclosure;

FIG. 11B is a plot of each instance of pressure detection by the fastadapting sensor and the slow adapting sensor in relation to the loadcell over time, obtained using the embodiment of FIG. 11A for a shorterperiod;

FIGS. 12A and 12C show photographic representations of flexible pressuresensors implemented with heterogeneous transduction profiles developedby altering the Young's modulus of elastomers used to construct themicro-pyramidal piezo-resistive sensors;

FIG. 12B shows a plot of resistance versus pressure in relation to FIGS.12A and 12C;

FIG. 13A shows a photographic representation of an array of pressure andtemperature sensors on a robotic effector in the shape of a human handin association with a cup of hot liquid, according to another embodimentof the apparatus of the present disclosure;

FIG. 13B shows a plot of resistivity versus temperature obtained usingthe temperature sensors of FIG. 13A;

FIG. 13C shows an optical microscopic image of one of the temperaturesensors of FIG. 13A;

FIG. 13D shows a plot of signature transmission rate versus temperatureof the temperature sensors of FIG. 13A;

FIG. 13E shows of an arrangement of resistive pressure and temperaturesensors on a single substrate;

FIG. 14A shows a diagram of indication signals versus time, obtained inthe application of FIG. 13A;

FIG. 14B shows a diagram of stimulus detection based on the indicationsignals shown in FIG. 14A;

FIG. 15A shows a spatiotemporal representation or pattern of tactilestimulus detection by fast adapting sensors, obtained using anotherembodiment of the apparatus of the present disclosure;

FIGS. 15B and 15C show diagrams of slip detection of different objects,using the apparatus of FIG. 15A;

FIG. 16A shows another arrangement with 69 fast adapting sensors in anexperiment of object feature classification;

FIG. 16B shows a result of the experiment of FIG. 16A, comparingperformance of the fast adapting sensors with that of slow adaptingsensors in local curvature classification;

FIGS. 17A to 17C show respective diagrams of classification accuracy forrespective objects of identical geometrical features and differenthardness values, in another application of the fast adapting sensors ofFIG. 16A;

FIG. 17D shows a diagram of classification accuracy for soft objects ofdifferent geometrical features;

FIGS. 18A and 18B show a conductive fabric of the apparatus of FIG. 1 inintact and damaged states, respectively;

FIGS. 19A and 19B show a mesh/planar conductor portion in twoalternative arrangements of the apparatus of the present disclosure,respectively;

FIGS. 20A and 20B show patterned wires in two alternative arrangementsof the apparatus of the present disclosure, respectively;

FIG. 21 shows nine sensor nodes with respective integrated fast adaptingsensors in three different spatial formations;

FIG. 22 shows a conductive fabric in intact and damaged states, andcorresponding pressure maps of pressure sensors associated with theconductive fabric, according to one arrangement of the apparatus of thepresent disclosure;

FIG. 23A shows conventional conductive traces in intact and damagedstates, and corresponding pressure maps of pressure sensors associatedwith the traces;

FIG. 23B shows a circuit diagram of the traces and the pressure sensorsof FIG. 23A;

FIG. 24A shows a signal diagram showing a ringing effect caused by anincrease in the number of sensor nodes; and

FIG. 24B shows a plot of pulse width versus the number of sensor nodes,in association with FIG. 24A.

DETAILED DESCRIPTION

FIG. 1 shows a schematic diagram of a sensor-based communicationapparatus 100 according to an embodiment of the present disclosure. Theapparatus 100 includes a communication medium 110 and a receiver 130. Inthis embodiment, the communication medium 110 includes a layer ofelectronic skin shown in FIG. 1 covering or worn by a robotic hand.

FIG. 2 shows an enlarged partial isometric view of the communicationmedium 110. The communication medium 110 includes a conductive fabric111 (e.g., a conductive substrate or medium) and a plurality of sensornodes 112 electrically attached to and embedded in the conductive fabric111. The sensor nodes 112 are associated with respective unique pulsesignatures 200 and are adapted to communicate with respective sensors113. In this embodiment, each sensor node 112 is integrally formed withthe corresponding sensor 113, although this may not be the case in otherembodiments. Each sensor 113 generates a sensory signal 113 a (seeFIG. 1) upon detecting a respective stimulus 113 b. In the presentembodiment, each sensor 113 is a tactile sensor responsive to a touch orpressure to generate the sensory signal 113 a. Each sensor node 112 istriggered, upon receipt of the corresponding sensory signal 113 a fromthe respective sensor 113, to transmit the associated unique pulsesignature 200 independently through a transmission medium shared by thesensor nodes 112. The transmission medium in this embodiment is theconductive fabric 111 of the communication medium 110. In otherembodiments, the transmission medium can be any medium shared by thesensor nodes 112. For example, the transmission medium may be onecapable of transmitting vibration/sound, optical, and/or magnetic fieldsignals.

In particular, referring to FIG. 3, each sensor node 112 furtherincludes a digital pulse generator 114 associated with the respectivesensor 113 (not shown in FIG. 3). The digital pulse generator 114includes a microcontroller 116 operatively associated with thecorresponding sensor 113, and a high-pass filter 117 arranged to filteran output of the microcontroller 116. For each sensor node 112, themicrocontroller 116 includes a digital I/O pin moveable between threepositions (“Vdd”, “High Z” and “Vss”) corresponding to positive, restingand negative potentials of the associated unique pulse signature 200,respectively (see FIG. 5). Instructions for generating pulses of theassociated unique pulse signature 200 is pre-programmed into themicrocontroller 116. The instructions specify a sequence of pulses and atime interval between each adjacent pulse pair. The microcontroller 116is triggered, upon receipt of the corresponding sensory signal 113 afrom the respective sensor 113, to generate the pulses of the associatedunique pulse signature 200 in real time by moveably switching thedigital I/O pin in accordance with the pre-programmed instructions. Thisoperation of the microcontroller 116 for signature generation based onthe sensory signal 113 a is indicated by the circle marked as “OP1” inFIG. 1. In one arrangement, the microcontroller 116 (Attiny20™ byMicrochip Technology™) includes a potential divider circuit forconverting a sensor resistance indicated by the respective sensorysignal 113 a into a voltage. The voltage is then sampled at 10 kHz witha 10-bit resolution by an onboard Analog-to-Digital Converter (ADC) ofthe microcontroller 116. The sampled values are sent to firmware modelsto mimic the fast-adapting (FA) or slow adapting (SA) behaviour ofreceptors found in the human skin, which is explained below. In otherembodiments, instead of using a microcontroller to generate therespective pulse signature 200, each sensor node 112 may use, forexample, a mechanical (MEMS) switch or a custom electrical circuit togenerate the respective pulse signature 200.

The high-pass filter 117 is arranged to filter or condition the pulsesgenerated by the microcontroller 116 to provide the corresponding uniquepulse signature 200 for transmission through a gain adjustment resistor115 associated with the respective sensor node 112 via the conductivefabric 111. The high-pass filter 117 includes two resistors and acapacitor. The resistors are electrically connected in series between apositive supply voltage source used for the positive potential (markedas “Vdd”) and a negative supply voltage source used for the negativepotential (marked as “Vss”). The capacitor has a first end electricallyconnected to the digital I/O pin through a node between the resistors,and a second end connected to the conductive fabric 111 through thecorresponding gain adjustment resistor 115. The high-pass filter 117 isthus used to filter any direct current (DC) and low frequency componentsin the respective unique pulse signature 200. The sensor nodes 112 mayadopt any other suitable circuitry for pulse generation and filtering.The circuitry illustrated in FIG. 3 is advantageous due to its lowercost and power consumption.

The unique pulse signatures 200 thus transmitted by the sensor nodes 112through the conductive fabric 111 are (or provide) a representation(e.g., a spatiotemporal representation) of a stimulus event associatedwith the stimuli 113 b detected by the corresponding sensors 113. Inthis embodiment, as illustrated in FIG. 1, the stimulus event is therobotic hand holding a ball. More particularly, the unique pulsesignatures 200 generated and transmitted by the respective sensor nodes112 collectively serve as a basis for acquisition of a spatiotemporalrepresentation of the stimulus event associated with the stimuli 113 bdetected by the corresponding sensors 113. With knowledge of locationsof the sensor nodes 112 (or the sensors 113) and the respective times oftriggering of the sensor nodes 112 (or of pressure detection by thesensors 113), a spatiotemporal representation of the stimulus event canbe accurately rendered. That is, the unique pulse signatures 200transmitted in association with a stimulus event carry or preserveinformation temporally descriptive of detection of the respectivestimuli by the respective sensors 113. Combined with knowledge oflocations (or relative locations) of the sensors 113 collocated with therespective sensor nodes 112, a spatiotemporal representation of sensorstimulation can be rendered.

FIG. 5 shows the unique pulse signature 200 transmitted by one of thesensor nodes 112 through the conductive fabric 111. In this embodiment,the unique pulse signature 200 is bipolar and transmitted independentlyand asynchronously by the respective sensor node 112. In this particularexample embodiment, each inter-pulse interval of each unique pulsesignature 200 has a unique duration (see FIG. 6), and the unique pulsesignature 200 has eight pulses, and a signature duration of 1 ms(millisecond), and the unique pulse signature 200 has a pulse durationof 60 ns (nanoseconds). Each neighbouring pair of pulses of each uniquepulse signature 200 has a unique duration in the apparatus 100. Thetotal number of voltage pulses in a pulse signature 200 denotes a‘weight’ of the pulse signature 200. The signature duration of 1 msspecifies a maximum allowed time difference from the first voltage pulseto the last voltage pulse of a pulse signature 200.

Referring again to FIG. 3, the apparatus 100 further includes a summingcircuit 120 electrically associated with the sensor nodes 112 and thereceiver 130. The summing circuit 120 includes an operational amplifier121 with a non-inverting input terminal that is grounded and aninverting input terminal that is electrically connected to theconductive fabric 111. The summing circuit 120 further includes aparallel connection of a resistor 122 and a capacitor 123 electricallyconnected across the inverting terminal and an output terminal of theoperational amplifier 121, with the output terminal being connected tothe receiver 130. With such a configuration, the summing circuit 120serves to filter or suppress any DC components in the unique pulsesignatures 200 transmitted by the sensor nodes 112 and also to ‘sum’ orcombine the unique pulse signatures 200 in time domain for transmissionthrough the conductive fabric 111 for receipt by the receiver 130. Thesumming circuit 120 may form part of the receiver 130 in otherembodiments. In such a configuration, the summing circuit 120 may clipany portions of the summed or combined signatures 200 exceeding supplyrails of the operational amplifier 121, provided that the time positionof each pulse in the summed or combined signatures 200 remainsunaffected by the clipping operation. Depending on implementation, thesumming circuit 120 may further include the resistors 115 and theconductive fabric 111, such that the summing circuit 120 may beconsidered to be distributed across the transmission medium. As shown inFIG. 2 with respect to one of the sensor nodes 112, in the distributedarrangement, the resistors 115 of the summing circuit 120 are arrangedproximate to the respective sensor nodes 112 and distal from the othercomponents 121-123 of the summing circuit 120. In the current embodimentof FIG. 3, the operational amplifier 121, the resistor 122 and thecapacitor 123 are disposed proximate or at the receiver 130 forconsideration of convenience, size and power constraints.

FIGS. 1 and 2 also show a representation of the unique pulse signatures200 independently transmitted by the sensor nodes 112 to collectivelyform an incoming signal 300 to be received by the receiver 130 via theconductive fabric 111 through the summing circuit 120. In the form ofthe incoming signal 300, the signatures 200 may be considered to becombined or superposed since they are independently and asynchronouslytransmitted when the corresponding sensor nodes 112 are triggered. Itcan be seen that the pulses in the incoming signal 300 are mostlystaggered. With reference to FIG. 4, the receiver 130 includes adetection and digitisation circuit 131 and a plurality of filters 132,which are digital filters in this embodiment. The detection anddigitisation circuit 131 is arranged to detect an edge in the incomingsignal 300, to activate the filters 132 upon edge detection, and toperform analog-to-digital conversion on the incoming signal 300 toprovide an intermediate signal 300′. With this configuration, thefilters 132 are activated only when an edge is detected in the incomingsignal 300 by the detection and digitisation circuit 131. Powerconsumption of the receiver 130 may thus be reduced. The receiver 130may thus be particularly suitable for use in scenarios of sparse orinfrequent stimulation events. As the transmitted signatures 200, asdiscussed above, are a representation of the stimulus event, theincoming signal 300 resulting from the transmitted signature 200 may beconsidered to be a representation of the stimulus event.

Each of the filters 132 is configured to detect the unique pulsesignature 200 of a respective one of the sensor nodes 112 in theintermediate signal 300′ to indicate a time of triggering of therespective sensor node 112 in association with the stimulus event.Specifically, each filter 132 is configured to perform a correlationoperation (e.g., convolution or multiplication in time domain) on theintermediate signal 300′ with the corresponding unique pulse signature200 to provide an indication signal 400 to indicate the correspondingtime of triggering of the corresponding sensor node 112 in the form of apulse (“indication pulse”, FIG. 4). This correlation operation isindicated by a circle marked as “OP2” in FIG. 1. The indication signal400 may be a continuous signal with the indication pulse at the time ofhigh correlation to indicate the generation of the sensory signal 113 aby the corresponding sensor 113. The indication pulse may be a positivepulse representing a binary ‘1’ or a negative pulse representing abinary ‘0’. In FIG. 4, two positive indication pulses and one negativeindication pulse are shown. In this example, irrespective of thepolarity, a pulse in the indication signal 400 indicates a detection oftactile pressure by the corresponding sensor 113. The unique pulsesignatures 200 may be pre-programmed into the receiver 130 for use bythe respective filters 132.

As illustrated in FIG. 4, the receiver 130 further includes a pluralityof threshold circuit 133 associated with the filters 132, respectively.Each threshold circuit 133 is configured to suppress an indication pulsein the corresponding indication signal 400 if the corresponding resultof correlation operation is below a correlation threshold value. Forexample, with an example correlation threshold value of 7 (e.g., if theintermediate signal 300′ correlates concurrently with at least sevenpulses of the respective signature 200 at a given time point), if theresult of a correlation operation for a signature is 6 (i.e., below thecorrelation threshold value), the indication pulse generated by thecorresponding filter is suppressed by the corresponding thresholdcircuit 133 due to the likelihood of error (i.e., low correlation). Thecorrelation threshold value may be adjusted based on statistic valuesof, for example, the filters 132. The indication signals 400 are thenreceived by a computing device 500 for storage, presentation or anyother use. Activation and deactivation of the threshold circuits 133 maydepend on those of the respective filters 132.

FIG. 7A shows three timing diagrams (i), (ii) and (iii) obtained usingthe apparatus 100 in another configuration involving six sensor nodes112 associated with respective unique pulse signatures 200 of 16 pulses.The top pulse diagram (i) shows the incoming signal 300 received by thereceiver 130 with the incoming signal 300 formed from pulse signatures200 transmitted by the six sensor nodes 112 illustrated in pulse diagram(ii). The bottom diagram (iii) shows the indication signals 400 of thefilters 132, with the correlation threshold values of the thresholdcircuits 133 marked by the dash horizontal line. In the bottom diagram,each small circle marks a respective time point of high correlationwhere a result of correlation of the intermediate signal 300′ with thecorresponding unique pulse signature 200′ exceeds the correlationthreshold value of the respective threshold circuit 133. It can beappreciated that the relative times of stimulus detection by therespective sensors 113 can be accurately determined or resolved based onthe respective time points (i.e., the respective indication pulses) ofhigh correlation. For instance, referring to FIG. 7A(iii), signaturetransmission by Node 4 occurs 4.9 μs earlier than that by Node 5. Aconventional time multiplexed system cannot achieve such a level oftemporal resolution without adopting a frame rate in the megahertzrange, which is not possible in most practical situations involvinglarge arrays of sensors. For instance, a conventional 256 element slipdetection array with a 1.9 kHz sampling rate is considered a very highspeed sensor array by the current standard, and can only achieve atemporal resolution of approximately 500 μs, which is at least 500 timesslower than the sampling rate achievable with the apparatus 100.

FIG. 7B is a diagram showing transmission of unique pulse signatures 200by five sensor nodes 112 in association with a stimulus event toillustrate the spatiotemporal nature of the stimulation event. By way ofillustration, the first pulse of each signature 200 is marked by ahollow circle AA, and each hollow circle AA is linked by a respectivedashed line BB to another hollow circle AA. This is an examplespatiotemporal representation of stimulation of respective sensors 112in association with the stimulus event (e.g., a touch). In thisparticular example, the unique pulse signature 200 of each sensor node112 begins with a positive pulse. The first pulse of each signature 200transmitted in association with the stimulus event can thus indicate arelative time point of triggering of the respective sensor node 112 bythe sensory signal 130 a of the respective sensor 113.

FIG. 7C shows the signatures 200 of FIG. 7B combined to form an incomingsignal 300 for receipt by the receiver 130. FIG. 7D shows indicationsignals 400 corresponding to the sensor nodes 112 of FIG. 7B, providedby the receiver 130 based on the incoming signal 300 of FIG. 7C. Foreach sensor node 112, each hollow circle AA marks a time point where aresult of correlation between the corresponding unique pulse signature200 and the intermediate signal 300′ exceeds the correlation thresholdvalue marked by the corresponding shaded area. Each hollow circle AA isshown to be connected by a respective dashed line BB to another hollowcircle AA to illustrate the spatiotemporal nature of the signal. It canbe appreciated that the relative time points of the hollow circles AA inFIG. 7D are similar or identical to those shown in FIG. 7B. This meansthat a spatiotemporal pattern of sensor stimulation can be representedwith reference to the time points of high signature correlation. Thus,with knowledge of physical locations of the sensors 113 (or of thesensor nodes 112), a spatiotemporal representation of the stimulus eventcan be rendered based on the relative time points of high correlation.

FIG. 8 illustrates an example spatiotemporal representation 600 of astimulus event associated with stimuli detected by the sensors 113 basedon the indication signals 400 in another scenario. In this example, thecommunication medium 110 is implemented in the form of electronic skin(or a thin glove) and is worn on the right hand of a human user pinchinga solid round object 190. Based on the indication signals 400 andknowledge of locations (either relative or absolute) of the sensor 113,times (or time points) of tactile pressure detection by the respectivesensors 113 can be spatiotemporally represented.

At time point t⁻¹, the communication medium 110 is not yet in contactwith the object 190. A non-detection status of each sensor 113 is markedby a small hollow circle 610.

At time point t₀, the communication medium 110 comes into contact withthe object 190, and a small portion of the sensors 113 detect tactilepressure as a form of stimulus 113 b, where a detection status of eachsensor 113 is marked by a small solid circle 620. For each sensor 113 ofthe detection status, the resultant indication pulse 630 in thecorresponding indication signal 400 is shown on a correspondinghorizontal line. A distance between the indication pulse 630 and thecorresponding solid small circle 620 along the corresponding horizontalline is proportional to an amount of elapsed time since pressuredetection by the corresponding sensor 113. That is, the indication pulse630 moves towards the right along the corresponding horizontal line astime passes.

At time point t₁, the communication medium 110 deforms and a largerportion of the sensor nodes 112 come into contact with the round object190, indicated by more indication pulses 630, 640. It can be seen thatthe indication pulses 630 generated by the small portion of the sensornodes 112 at time to have moved further to the right, indicating thatmore time has elapsed since the pressure detection by the sensors 113 ofthose indication pulses 630.

At time point t₂, the communication medium 110 deforms more as the gripforce on the round object 190 increases and an even larger portion ofthe sensor nodes 112 come into contact with the object 190, indicated byeven more indication pulses 630-650. A clear spatiotemporal patternformed by the generated indication pulses 630-650 and representing thestimulus event of pinching the round object 190 can be clearly observed.

FIG. 9A shows another pulse signature with 14 pulses (weight, W, of 14)after quantisation, with the first pulse marked by a rectangular box.‘V+’ and ‘V−’ mark the quantization thresholds for pulse detection,respectively.

FIG. 9B shows a diagram of temporal precisions of the indication signals400 versus numbers of overlapping pulse signatures 200, for differentnumbers of pulses (or weights, W) in each signature 200, obtained with240 sensors in an actual experiment. The shaded regions indicaterespective standard deviations. The output of the receiver 130 maintainsthe relative time differences of the transmitted unique pulse signatures200 with a temporal precision of 60 ns or less. The transmission latencyis also constant, dependent only on the duration of the pulse signature200 and not the number of sensor nodes 112.

FIG. 9C shows relationships between correlation threshold values anddetection error probabilities (transmission error rate) with a weight,W, of 10. With 240 simultaneously transmitting sensor nodes 112(simultaneous transmission for ensuring the occurrence of collision) anda correlation threshold value of 6, a false positive probability of0.000023 (0.0023%) and a missed detection probability of 0.00031(0.031%) can be achieved. Using a Monte Carlo simulation, even with 1000overlapping signatures 200, it is possible to achieve a probability offalse positive detection of 0.024 (or 2.4%) or a probability of misseddetection of 0.0021 (or 0.21%). Given the typically sparse nature oftactile events, the probability of 1000 overlapping signatures 200 isexpected to be low. The dashed lines in FIG. 9C represent simulationresults. The result of FIG. 9C is obtained, with a 95% confidencebounds. In the simulation of FIG. 9C, each sensor node 112 transmits asingle symbol (i.e., pulse). The extent of overlap between any twosymbols takes a uniform random distribution from a minimum of 1 pulsewidth to a maximum of the entire signature duration. The polarity of thetransmitted symbol is also randomly assigned. The codes (i.e.,signatures 200) used in this simulation have a maximum auto andcross-correlation value of 2. Pulse widths are of 60 ns in duration andall pulse signatures 200 have a duration of 1 ms. 100,000 Monte-Carlotrials are conducted for each combination of signature weights (i.e.,the number of pulses in each signature 200) and number of sensor nodes.

FIG. 9D shows a diagram of Signal to Interference and Noise Ratio (SINR)of the output (i.e., the indication signals 400) of the receiver 130versus the number of overlapping signatures 200 with a weight, W, of 10and a pulse width of 60 ns. In FIG. 9D, the dashed line indicatesresults by Monte-Carlo simulation and the line marked by squaresindicates actual results and shows a trend similar to that of the dashedline.

FIG. 9E shows a diagram of SINR of the output of the receiver 130 versusthe number of overlapping signatures 200, obtained for different pulsewidths using simulation. It can be appreciated that the SINR of theoutput of the receiver 130 can be improved by reducing the pulse widthor duration.

FIG. 9F shows a diagram of SINR of the output of the receiver 130 versusthe number of overlapping signatures 200, obtained for different weights(i.e., numbers of pulses in each signature 200) using simulation basedon a pulse width of 60 ns. While larger signature weights (W) improvesSINR substantially where the number of overlapping signatures is lessthan 100, the opposite is true where the number of overlappingsignatures is higher. Therefore, a weight of 10 may be optimal.

The SINR characterizes the separability of a stimulus detection frominterference, based on the output of the receiver 130. In an experiment,a physical hardware test setup with an array of two hundred and fortysensor nodes, each programmed with a unique pulse signature, isdeveloped to determine the SINR. Each trial begins with an externaldigital edge signal that is broadcast to all sensor nodes to triggeringthe sensor nodes to transmit the respective pulse signatures after arandom delay of less than 1 ms. This ensures that the two hundred andforty transmitted signatures will overlap at varying temporal offsetsbetween trials. For trials involving less than two hundred and fortysensor nodes, the excluded sensor nodes may be programmed to ignore thetrigger.

Sixteen of the two hundred and forty sensor nodes have probes attachedto their transmission pins (digital pins), respectively. Signals fromthese probes serve as the ground truth on the actual time and polarityof the pulses transmitted. The digital signals from these sixteenprobes, as well as the combined pulse signatures from the two hundredand forty sensor nodes are digitized at 125 MHz simultaneously by amixed signal oscilloscope (Picoscope 3406D), thus ensuring that allchannels are synchronized in time.

The SINR is computed for the receiver 130 associated with the sixteenprobed sensor nodes. An interference value is computed as theroot-mean-squared (RMS) value of the receiver output as thecorresponding sensor node transmits its pulse signature. The last 100 nsof the receiver output is excluded from the RMS computation, since itcorresponds to the detection of the correct pulse signature and shouldnot be considered as interference. SINR is then computed as the ratiobetween the signature weight W and the interference value. For eachnetwork size, 1000 trials were conducted, and the reported SINR isaveraged from the 16 receivers across all 1000 trials.

Timing precision is obtained as the difference in time between the startof last pulse transmission, as obtained from the attached probe, and thetransmission time as determined from the output of the receiver. Thereported timing precision in FIG. 9B is obtained as an average acrossall the 1000 trials for each network size.

FIG. 10 shows a flowchart of an example algorithm or method 1000 whichmay be used for generating the pulse signatures 200 for the apparatus100. The method 1000 includes steps 1010 to 1040, where step 1020includes sub-steps 1021 to 1026.

Step 1010 includes creating a database to store the unique pulsesignatures 200 to be associated with the sensor nodes 112, and isfollowed by step 1020.

Step 1020 includes generating a family or set of signatures 200 byperforming sub-steps 1021 to 1026.

Sub-step 1021 includes determining whether enough pulses have beengenerated to form a unique signature 200 of a specified weight, endingstep 1020 and proceeding to step 1030 if affirmative, and proceeding tosub-step 1022 if otherwise. The effect of the determination of sub-steps1021 is to ensure that the pulse positions of the signature 200 beinggenerated are iteratively searched to make sure that duplicate temporalfeatures are not used within the family of signatures 200 and that thepulse sequence being generated meets the specified weight.

Sub-step 1022 includes adding a new pulse at random time within thespecified signature duration, and is followed by sub-step 1023.

Sub-step 1023 includes checking the pulse sequence of the currentsignature 200 being generated against the created database for anyduplicate sequence in the database, and is followed by sub-step 1024.

Sub-step 1024 includes determining whether a duplicate sequence has beenfound in the database in sub-step 1023, proceeding to sub-step 1025 ifaffirmative, and proceeding to sub-step 1026 if otherwise.

Sub-step 1025 includes removing the most recently added pulse in thesignature 200 being generated, and is followed by sub-step 1022.

Sub-step 1026 includes updating the created database with the currentpulse sequence as a new signature 200 (i.e., adding the current pulsesequence as a new signature 200), and is followed by sub-step 1021. Theeffect of sub-step 1026 is to update the database with the current pulsesequence resulting from the addition of the current pulse, so that, ifthe next determination in sub-step 1021 is negative, the search for thenext pulse position in sub-step 1022 uses the current pulse sequence inthe updated database.

In such a manner, each signature 200 generated in step 1020 is unique inthe database.

Step 1030 includes determining whether a new signature 200 has beenfound, proceeding to step 1040 if affirmative, and proceeding back tostep 1020 if otherwise.

Step 1040 includes determining whether enough signatures 200 have beenfound for the sensor nodes, ending the process if affirmative, andproceeding back to step 1020 if otherwise.

Step 1030 may be combined with step 1040 if step 1020 is modified toiterate an endless loop for signature generation, to be terminated aftera certain period of time to start over. It is envisaged that some of thesteps and sub-steps of the method 1000 may be modified, combined, oromitted, provided that unique pulse signatures 200 can be generated.

With the use of this algorithm of FIG. 10, autocorrelation andcross-correlation may be reduced whilst allowing enough unique pulsesignatures 200 to be assigned to the sensor nodes 112. With the numberof signatures 200 being larger than or equal to the number of the sensornodes 112, a family of pulse signatures may be characterized by threeparameters Φ(F, ω, λ), where:

-   -   F is the duration of each pulse signature in the family,    -   ω is the number of pulses per signature, and    -   λ is the maximum allowed interference between signatures within        the family.

With F and ω determined, the temporal position of each individual pulsein each signature can then be determined to meet λ. For the computationof λ, consider two pulse signatures, s and s′, both with ω=4 and havingpulses at times {τ₁, τ₂, τ₃, τ₄} and {τ′₁, τ′₂, τ′₃, τ′₄} respectively.Convolution of s with s′ results in at least 1 overlapping pulse, givingλ≥1. However, the pulse signatures can be designed to have, at most, oneoverlapping pulse. This can be achieved by ensuring that eachinter-pulse interval in each pulse signature is unique, as is the casewith the embodiment of FIG. 1. In the case of s and s′, there are ⁴C₂(i.e., six) inter-pulse intervals per signature. To achieve λ=1, all 12inter-pulse intervals (from s and s′) must be unique.

Expanding to a case where λ>1, the concept of temporal pulse featuresP_(λ) is introduced. For example, if λ=2, the feature P₂ will have twoelements {ρ₁, ρ₂}, where ρ₁ and ρ₂ are an ordered pair of inter-pulseintervals. In the case of s and s′, there are ⁴C₃ (i.e., four) P₂features per signature. To ensure λ=2, all P₂ features in the familyshould be unique. The same approach can be applied to cases of λ>2. Anexample of pulse signatures at two different nodes is illustrated inFIG. 6. An apparatus with a theoretical probability of error of zero canbe achieved by ensuring that ω>nλ, where n is the number of signaturesin the family. The design of the pulse signatures is discussed infurther details below.

In the example of FIG. 1, each sensor 113 only needs to indicate onestate of detection in its sensory signal 113 a upon pressure detection.Accordingly, each sensor node 112 is correspondingly associated with oneunique pulse signature 200 to indicate the state of detection, and therespective filter 132 is also associated with the corresponding uniquepulse signature 200 to perform the needed correlation operation. As aresult, with each pressure detection by the sensor 113, an indicationpulse 400 of either polarity is generated to indicate the state ofdetection by the respective sensor 113. For this particular example,polarity of the indication pulse may not represent useful information.However, in other embodiments, the polarity may be relevant. Forexample, two pulse signatures 200 of the same pulse positions anddifferent (e.g., opposite) pulse polarities may be used by each sensornode 112 to indicate respective two states in the corresponding sensorysignal 113 a. The polarity of each pulse, or “pulse polarity”, means thepotential of the pulse, either the positive voltage potential (“Vdd”) orthe negative voltage potential (“Vss”). For parallel correlationoperations, the number of filters 132 should match the total number ofunique pulse signatures 200 assigned to the sensor nodes 112.

It would be appreciated that the sensor nodes 112 may be associated withany other types of sensors 113, such as temperature sensors, which maybe integrated with the respective sensor nodes. Further, the sensornodes 112 may be associated with more than one types of sensors (e.g.,pressure and temperature sensors). For example, in an electronic skinapplication, the sensors 113 include an array of fast-adapting (FA)pressure sensors, slow-adapting (SA) pressure sensors and temperaturesensors. Together, these sensors 113 may be configured to mimic thebiological counterparts.

The FA sensors 113 are configured to respond only to dynamic deformationof the conductive fabric 111 and to be insensitive to static forces.Each FA sensor 113 is configured to indicate a first state of pressureincrease and a second state of press decrease in its sensory signal 113a. That is to say, for each FA sensor 113, the sensory signal 113 agenerated by the FA sensor 113 has the first and second states. Thecorresponding sensor node 112 of each FA sensor 113 is associated withfirst and second unique pulse signatures 200 to indicate the first andsecond states of the sensory signal 113 a, respectively. Specifically,with the firmware of the sensor node 112 configured to recognise thecorresponding FA sensor 113, the firmware model in the sensor node 112for the FA behaviour causes the microcontroller 116 to generate andtransmit the first and second unique pulse signatures 200 according tothe state of the corresponding sensory signal 113 a. Each sensor node112 is triggered, upon receipt of the corresponding sensory signal 113 ain the first state, to transmit the associated first unique pulsesignature 200, and upon receipt of the corresponding sensory signal 113a in the second state, to transmit the associated second unique pulsesignature 200 independently through the transmission medium. Morespecifically, in one particular example, the microcontroller 116 iscaused by the firmware model to generate and transmit the first uniquepulse signature 200 for each increment of more than 50 mV detected inthe corresponding sensory signal 113 a, and to generate and transmit thesecond unique pulse signature 200 for each decrement of more than 50 mVdetected in the corresponding sensory signal 113 a. With such aconfiguration, the sensor node 112 of each FA sensor 113 is able toindicate to the receiver 130 the state of the sensory signal 113 a(increase and decrease of pressure). Moreover, as discussed above, thefirst and second unique pulse signatures 200 of each sensor node 112 mayhave different (e.g., opposite) pulse polarities. That is to say, thefirst and second pulse signatures 200 may have the same pulse positionsbut opposite pulse polarities (i.e., voltage potentials). In otherembodiments, the first and second signatures 200 may be partially orcompletely different in terms of, for example, pulse position, pulseduration, inter-pulse duration, pulse polarity, the number of pulses, ora combination thereof. Contrary to the biological counterparts which donot distinguish between pressure increase and pressure decrease, thearrangement of the FA sensors 113 and the respective sensor nodes 112can meet a wide range of temporal response requirements, from precisepressure or force measurements to transient tactile stimulus detection.Each sensor node 112 may, in other arrangements, be associated with asensor 113 of any type, and be associated with unique pulse signaturescorresponding in number to states of the sensory signal 113 a generatedby the sensor 113.

The SA sensors 113 are further configured to respond to static pressureand to be insensitive to dynamic deformation of the conductive fabric111. Each SA sensor 113 is configured to indicate a current value ofstatic pressure in its sensory signal 113 a, and the correspondingsensor node 112 transmits the corresponding signature 200 at a frequencydependent on the current value. In this embodiment, the signaturetransmission frequency is in a positive relative to the current value ofdetected static pressure in the sensory signal 113 a. That is, thehigher the current value of detected pressure, the shorter the intervalbetween two corresponding consecutive signature transmissions. Inparticular, the firmware model for SA behaviour causes themicrocontroller 116 to generate and transmit multiple instances of therespective unique pulse signature 200 with an interval proportional tothe 8 point averaged ADC digital value. For FIGS. 11A, 11B and 14B, theinterval is the sum of 1 ms and a product of 100 μs and the converteddigital value in decimal. For example, to represent a value of 500, twoconsecutive signatures are transmitted with an interval of 51 ms(500×100 μs+1 ms). Together with a 1 ms pulse signature duration, amaximum ADC value of 1023 will correspond to a 103.3 ms interval betweentwo consecutive signatures. The sensor node 112 of each SA sensor 113needs to be associated with one unique pulse signature 200 to indicate acurrent value of detected pressure in its sensory signal. To indicatethe current value, the associated sensor node 112 is configured to,having transmitted a previous one of an assigned unique pulse signature200, transmit a current one of the same unique pulse signature 200 toindicate the current value of detected static pressure by the intervalbetween the transmitted current and previous ones of the assignedsignature 200. Upon initiation where the sensor node 112 has nottransmitted the assigned signature 200 in association with a stimulusevent, the sensor node 112 may indicate a first value of detectedpressure by consecutively transmitting two instances of thecorresponding signature 200 with an interval corresponding to the firstvalue. Any subsequent values of detected static pressure may beindicated by the sensor node 112 in the manner described above. Eachsensor node 112 may, in other arrangements, be associated with a sensor113 of any type, and be configured to transmit consecutive instances ofan associated unique pulse signature 200 to indicate, by a correspondinginterval between current and previous ones of the associated uniquepulse signature 200, a current value of the sensory signal 113 agenerated by the sensor 113.

It is worth noting that each sensor node 112 is, in the example of FIGS.11A and 11B, configured by way of firmware to recognise and beassociated with the respective sensor 113. That is, the sensor node 112chooses a mode of operation based on the type or configuration of theassociated sensor 113 (SA or FA). Whilst the FA and SA sensors 112 aredescribed to be different types of sensors, they may be implementedusing the same component (e.g., a piezoresistive element). In such acase, whether the sensor 112 is to function or be treated as an FAsensor or an SA sensor can be determined by the firmware of therespective sensor node 113.

In another embodiment, each sensor node 112 is configured to transmitanother associated unique pulse signature 200 independently through thetransmission medium to indicate an internal state of the respectivesensor node. For example, the sensor node 112 may be associated with oneor more additional unique pulse signatures for each additional internalstate to be reported.

FIG. 11A shows a plot of dynamic force increases and decreases sensed byone of the FA sensors 113 in relation to a load cell over time, and aplot of static forces detected by one of the SA sensors 113 against theload cell over time, obtained based on the corresponding indicationsignals 400 shown in FIG. 11B. For the FA sensor 113, the detectedstates of force increase and force decrease are marked by oppositerespective triangular symbols. For the SA sensor 113, the values ofdetected static force are marked by respective square symbols. In theexample of FIGS. 11A and 11B, the SA sensors 113 can accurately detectstatic force and indicate the respective detected values in theirrespective sensory signals 113 a. The FA sensors 113 can accuratelydetect dynamic force and indicate the detected states of force increaseand force decrease in their sensory signals 113 a. This is demonstratedin FIG. 11A, where the FA sensor 113 successfully detects force changesassociated with a prick from a lancet lasting about 1 ms. The SA sensor113 in this embodiment is not sensitive enough to detect the prickbecause the duration of the prick of 1 MS is well below thecorresponding interval for indication of the force intensity. Both theSA and FA sensors 113 successfully detect a finger press taking placeprior to the prick, as shown in FIGS. 11A and 11B. The readings of theload cell are smoothed using a moving average filter of 8 points(OriginLab 2017). It should be noted that the term “force” as used inthis context may be interpreted to include “pressure”.

FIGS. 12A and 12C show photographic representations of flexible pressuresensors implemented with heterogeneous transduction profiles developedby altering the Young's modulus of elastomers used to construct themicro-pyramidal piezo-resistive sensors. FIG. 12B shows a plot ofresistance values versus pressures. This allows sensors of varioustactile sensitivities to be distributed spatially on the same substrate(i.e., the conductive fabric 111). With such a construction, the sensorscan be made to be sensitive to both light touches and higher loadswithout saturation. The wide dynamic pressure range enables continuedpressure detection under typical manipulation forces when gripping anobject.

FIG. 13A shows a photographic representation of an array of pressure andtemperature sensors on a robotic effector in the shape of a human handin association with a cup of hot liquid. FIG. 13B shows a plot ofresistivity versus temperature obtained using the temperature sensors ofFIG. 13A. FIG. 13C shows an optical microscopic image of one of thetemperature sensors of FIG. 13A. The temperature sensors are flexibleresistive sensors implemented on a single substrate (i.e. conductivefabric). The temperature sensor is designed to have a main sensitivityrange from 20° C. to 50° C., which similar to the cold receptorafferents in human skin. The associated sensor node transmits the uniquepulse signature at a reduced frequency (i.e., increased interval) as thedetected temperature rises above 25° C. (see FIG. 13D). FIG. 13E showsan example arrangement of resistive pressure and temperature sensors ona single substrate (i.e., conductive fabric). FIGS. 14A and 14B showdiagrams in relation to the application of FIG. 13A (holding a cupcontaining hot liquid). FIG. 14A shows a diagram of indication signalsversus time obtained from pulse signatures transmitted by thetemperature and pressure (SA) sensors. FIG. 14B shows a diagram ofstimulation detection based on the indications signals shown in FIG.14A. It can be seen from these figures that simultaneous or nearsimultaneous detection of tactile and thermal stimuli by the SA andtemperature sensors can be achieved.

In another application, the FA sensors 113 can be employed by, forexample, a robotic effector to detect slippage of an object held by theeffector. FIG. 15A (part i) shows a spatiotemporal representation orpattern of tactile stimuli detected by the FA sensors 113 over time,with the FA sensors 113 provided on the effector. A spikingconvolutional network is implemented to compute the magnitude anddirection of slippage in an event-driven manner. As slippage of theobject starts to occur, stimulus detection by the FA sensors 113triggers the computation of movement to estimate the onset of slippage.

Referring to FIG. 15B, movement estimates can be calculated immediatelyupon slippage onset, and the downward movement of the object can beaccurately identified. FIG. 15C shows that the same implementation canbe used to detect the slippage of a needle with 1 ms of latency.However, the directional estimates show higher deviations due to thesmaller number of stimulated FA sensors 112 and the reduced contactarea. Higher sensor densities are thus required for dextrousmanipulation tasks of varying object form factor.

Specifically, in the experiments of FIGS. 15A, 15B and 15C, an acrylicdisk of 1 cm diameter and a needle of 0.8 mm diameter is heldrespectively and vertically between two flat opposing surfaces of abench vice. An array of 80 pressure sensors (similar to the one in FIG.14A but without the thermal sensors), are arranged to interface with acorresponding array of sensor nodes mimicking FA behaviour. The sensorsare pasted on one of the surfaces of the vice. A thread connects theobject to a load cell. A separate thread is connected to the oppositeside of the load cell and adapted to be pulled to cause slippage of theobject from the vice. Data generated by the 80 sensor nodes is sampledtogether with an analog output of the load cell at 125 MHz using anoscilloscope (Picoscope 3406D). Computation of slip detection isprocessed offline in MATLAB.

The computation of local movement estimates (part ii, FIG. 15A) isgenerally as follows:

-   -   1. For an event from a particular sensor A that occurred at t₀,        look for prior events from sensor within distance D of sensor A        that occurred at t_(prior) where t₀−Δt<t_(prior)<t₀;    -   2. For each prior event, compute movement magnitude

${{Magnitude} = \frac{D}{t_{0} - t_{prior}}};$

-   -   3. Movement direction for each prior event

direction=a tan 2(d _(y) ,d _(x))

-   -    where d_(x) and d_(y) are the x and y components of the        distance D; and    -   4. By averaging the magnitude and direction for each prior        event, the local movement estimate at sensor A's location is        obtained.

The global movement estimate (part iii, FIG. 15A) is obtained as themoving average (exponential kernel of 5 ms time constant) for all thelocal movement estimates. For FIGS. 15B and 15C, Δt=5 ms and D=2 mm.

FIGS. 16A and 16B show another application where an array of 69 FAsensors mimic Meissner corpuscle responses. It can be appreciated thatvarious local curvatures can be classified up to 10 times faster (within7 ms with a 97% accuracy) than possible with a 100 frame-per-second(fps) conventional sensor array.

Each of FIGS. 17A to 17C shows a diagram of classification accuracy fortwo objects of identical geometrical features and different hardness, inanother application of the FA sensors of FIG. 16A. FIG. 17D shows adiagram of classification accuracy for soft objects of differentgeometrical features of the same hardness. The results demonstrate theimportance and effectiveness of temporal features in rapid tactilediscrimination.

FIGS. 18A and 18B show the conductive fabric (or conductive substrate)111 of the communication medium 110 in intact and damaged states,respectively. It can be seen that signal communication of the sensornodes 112 through the conductive fabric 111 remains unaffected despitetwo tears formed in the conductive fabric 111 (labelled as “Torn edges”in FIG. 18B). A signal conducting path between the receiver 130 and amost distal one of the sensor nodes 112 is shown (marked as “Signal pathremains”). Also shown in FIG. 18B is a removed portion of the conductivefabric 111 (labelled as “Hole in substrate”). Two of the sensor nodes112 (marked by respective dashed squares and labelled as “Nodesremoved”) corresponding to the removed portion are removed altogether. Askilled person would appreciate that the conductive fabric 111 thusprovides multiple signal conducting paths between the receiver 130 andeach of the sensor nodes 112. Importantly, communication is adverselyaffected only if all signal conducting paths between the receiver 130and the respective sensor node 112 are lost. That is to say,communication of a sensor node 112 in a portion of the conductive fabric111 remains unaffected unless the portion of the conductive fabric 111is completely torn apart or otherwise removed from the remaining portionof the conductive fabric 111. In most cases, a partial tear in theconductive fabric 111 would not adversely affect communication of thesensor nodes 112 via the conductive fabric 111. That is, signalcommunication between each of the sensor nodes 112 and the receiver 130remains unaffected provided that the conductive fabric 111 can stillprovide at least one signal conducting path between the respectivesensor node 112 and the receiver 130. Communication of the sensor node112 is thus robust to damage (e.g., physical damage) of the conductivefabric 111.

In the example of FIGS. 18A and 18B, the conductive fabric 111 is madeof a conductive polymer (e.g., PEDOT:PSS). However, in otherembodiments, any conductive medium (e.g., conductive knitted wires,carbon based nanomaterials, metal nanowires, metal films, and metalwires) may be used in place of or in conjunction with the conductivefabric 111. The conductive fabric 111 of this example is electricallyconnected to the sensor nodes 112. It is to be emphasized that theconductive fabric 111 is just one possible form of the conductivemedium. Some other example forms are described below with reference toFIGS. 19 and 20. By virtue of the polymer configuration, the conductivefabric 111 provides (or can be considered to provide) multiple signalconducting paths for each of the sensor nodes 112 and, in thisembodiment, also acts as a structural support to support the sensornodes 112. The conductive fabric 111 is elastic and flexible, thussuitable for electronic skin applications. The conductive fabric 111thus allows for a flexible arrangement of the sensor nodes 112, andsignal communication is resistant to or unaffected by damage sustainedby the conductive fabric 111. The sensor nodes 112 can be flexiblyconfigured in terms of placements, density and distribution to meetvarious design and application requirements. The conductive fabric 111is thus suitable for covering or providing, for example, a curvedsurface of a humanoid robot for sensing non-uniform features.

FIG. 19A illustrates another communication medium 110′ which is avariant of the communication medium 110. This communication medium 110′includes a mesh/planar conductor portion 111′ associated with the sensornodes 112. In this example, each sensor node 112 is powered by arespective power source (e.g., a battery). Communication between eachsensor node 112 and the receiver 130 remain unaffected so long as atleast one signal path exists therebetween. In addition, the mesh/planarconductor portion 111′, if made to be elastic, are easier to realise incomparison with patterned wires (see FIGS. 20A and 20B). Similar to thepolymer configuration of FIGS. 18A and 18B, the mesh/planar conductorportion 111′ provides substantial redundancy in signal conducting pathsbetween each sensor node 112 and the receiver 130.

The sensor nodes 112 in the example of FIG. 19B wirelessly harvest powerfrom a source 140 of electromagnetic waves (e.g., power transmissioncoils), which may be incorporated in an underlying rigid structure of,for example, a robotic/prosthetic body portion, enabling flexibledistribution of the sensor nodes 112 along the mesh/planar conductorportion 111′. The sensor nodes 112 in other embodiments may also beconfigured to harvest power in a similar manner. In addition, otherforms of power harvesting techniques (mechanical, solar, chemical, andthermal, etc) may also be employed to power the sensor nodes 112wirelessly. The sensor nodes 112 may also be provided with respectivepower storage means (e.g., a rechargeable battery or a capacitiveelement) to store the harvested power.

FIGS. 20A and 20B show two alternative embodiments of a basic setup ofthe communication medium 110″ where sensor nodes 112 are embedded inelastomeric material. In the embodiment of FIG. 20A, the sensor nodes112 are powered by a common power supply. Each of the sensor nodes 112and the receiver 130 is connected by a respective conductor 111″ (e.g.,a wire) connecting to a common connection node. In such a configuration,each sensor node 112 requires only a single conductor 111″ forcommunication. The configuration of FIG. 20B differs from that of FIG.20A only in that each sensor node 112 is associated with a respectivepower source (e.g., a battery). Although this configuration of theconductor 111″ reduces wiring complexity by virtue of the commonconnection node, it is not as robust as the configurations of FIGS. 18Ato 19B in terms robustness of signal communication to damage.

It should be appreciated that, in other embodiments, the conductivemedium may include at least one of a conductive fabric, a conductivebulk conductor, a conductive substrate, a conductive solid, a conductivegel, and a conductive fluid. An example of conductive fluid isGalinstan, a liquid metal made from gallium, indium and tin. It ispossible to construct a mesh of micro-fluidic channels in a stretchablepolymer and fill it with Galinstan to achieve a highlyflexible/stretchable substrate.

Wiring simplicity in certain applications (e.g., e-skin) is critical,especially when wires are to be routed along non-uniform surfaces orcurvatures. FIG. 21 shows nine sensor nodes with respective integratedFA sensors in three different spatial formations, placed on a conductivefabric (knit jersey conductive fabric, Adafruit) and powered byrespective internal batteries. In each of the irregular formations, theFA sensors can accurately detect respective stimuli, allowing aspatiotemporal representation to be obtained and demonstrating theability of the sensor nodes to be used in environments of non-uniform oruneven geometries. In particular, to apply pressure, a conductive rod350 is pressed against some of the sensors in each arrangement. Theconductive rod 350 provides a charge return path, such that charges fromthe environment can flow back to the sensors by coupling with a humanhand operating the conductive rod. The same effect may be achievedthrough the use of a grounded conductive encapsulant.

FIG. 22 shows, on the left, an intact state (top) and a damaged state(bottom, showing three cuts) of a communication medium of sixteen sensornodes with respective integrated sensors, arranged in a grid formation.Shown on the right are corresponding representations of pressuredetected by each sensor node in the intact state (top) and the damagedstate (bottom), respectively. As discussed above in relation to FIGS. 18to 20, the conductive fabric 111 or the mesh/planar conductor portion111′ provides redundant signal paths, allowing communication of thesensor nodes to remain unaffected even when the conductive fabric 111 orthe mesh/planar conductor portion 111′ is in the damaged state. Incomparison, communication capability of an array of 16 sensors placed ona conventionally implemented row and column traces is significantlyimpaired when the traces are in a similar damaged state of three cuts(see FIGS. 23A and 23B).

The temporal precision of a sensor node 112 is limited mainly by theduration of a single voltage pulse. As more sensor nodes 112 are addedto the array, the capacitance of the electrical conductor through whichthe pulses propagate also increases. The increased capacitance resultsin a reduced phase margin of the op-amp feedback loop (i.e., the summingcircuit 120) and causes ringing in the output (FIG. 24A). The ringingcan be reduced by increasing the feedback capacitance C_(F) (i.e., thecapacitance of the capacitor 123, FIG. 3) to improve stability. However,the pulse width will increase as a result (FIG. 24B). A SPICE simulation(Cadence® Spectre®) is used to determine how the pulse width changeswith an increasing number of sensor nodes. The output of each sensornode 112 is modelled as a voltage source with a square wave. The edgesof the waveform are high pass filtered to obtain the waveform of thevoltage pulse (FIG. 24A). A transient simulation is run for N=200 to16000. For each N, the value of C_(F) is swept to find the minimum C_(F)that has acceptably low levels of ringing where the overshoot does notexceed quantization threshold set at 40% of pulse amplitude. Finally,F_(sample) is obtained as the reciprocal of the resultant pulse width,taken to be the length of time in which the voltage remains abovequantization threshold.

As discussed above, the signatures associated with the sensor nodes aredesigned to be sent independently (asynchronously) with a highprobability of correlation at the respective filters. Each pulsesignature consists of W voltage pulses spaced apart at specific timeinstancesτ={τ₁, τ₂ . . . τ_(m)}. At the receiving end, pulses arereceived at time instances τ′={τ′₁, τ′₂ . . . τ′_(w)}. The receiverfinds the intersection τ=(τ∩τ′) where the cardinality /T/ denotes thecorrelation strength. If the correlation strength exceeds a predefinedthreshold (i.e., the correlation threshold value), a signature is deemedto have been correlated by the respective filter.

An ideal set of pulse signatures is one that has minimal autocorrelation(correlation between a particular signature and its time-shiftedversions) and cross-correlation (correlation between a particularsignature and other signatures in the set). There should also be enoughunique signatures in the set to identify all sensor nodes in the array(cardinality). As discussed above, a family of pulse signatures may becharacterized by the same 3 parameters:

-   -   F=the maximum number of pulses that fit within the duration of a        signature;    -   ω=weight or the number of pulses per signature; and    -   λ=maximum allowable interference (autocorrelation and        cross-correlation) between two signatures.

For a pulse signature with a signature duration (Ts) of 1 ms and a pulseduration (Tp) of 100 ns:

$F = {\frac{Ts}{Tp} = 10000}$

Parameters ω and λ are closely related to the error performance of thereceiver. Under ideal conditions, all ω voltage pulses of the targetsignature should be successfully correlated, and thus ω is the maximumcorrelation. λ is the maximum cross-correlation allowed betweensignatures of the same family. If N non-target signatures overlap withthe target signature, the amount of interference could be as high asN×λ. Error performance will thus degrade if N×λ is much larger than ω.

The number of unique pulse signatures must match that of the sensornodes. To accommodate for thousands of the sensor nodes, the pulsesignatures may be configured to have λ=2 such that the number ofsignatures (C) satisfies:

$C \leq \frac{\left( {F - 1} \right)\left( {F - 2} \right)}{{\omega \left( {\omega - 1} \right)}\left( {\omega - 2} \right)}$

Therefore, with F=10000 and ω=10, the array can accommodate up to138,847 sensor nodes, which should be sufficient in most cases for wholebody robot sensor skins. As described above, the pulse signatures areelectrical and can be either positive or negative (i.e., have positiveor negative pulses), which allows each signature to take on severalvariants. For instance, two signatures of the same pulse positions andopposite pulse polarities may be considered to be two states or variantsof a single signature, for indicating a binary ‘1’ and a binary ‘0’,respectively. With such a consideration, a single signature may be usedby a FA sensor to indicate, using the two states or variants of thesignature, an increase and a decrease in pressure. This is not possiblewith Optical Code Divisional Multiple Access used in fibre opticcommunication, which requires complicated optical devices for signalgeneration and transmission.

Some advantages of the present disclosure are discussed below.

Stimuli of a stimulus event can be sparse or dense. To achieve anaccurate spatiotemporal representation of the stimulus event (e.g.vision, hearing, taste, touch, smell, etc.), sensory signals must begenerated and transmitted with a high temporal resolution. The apparatus100 is well suited for such tasks. Firstly, sensory signals generated bythe respective sensors 113 are transmitted by the respective sensornodes 112 in the form of respective unique pulse signatures 200 throughthe conductive fabric 111. The process does not require any complexcircuitry for digitisation. Further, the sensor nodes 112 do not requireany implementation of synchronization or collision sensing. Further, nocommon signal ground is needed. The sensor nodes 112 can transmitrespective unique pulse signatures 200 independently at any instancewith minimal communication overhead. Contrary to conventionalframe-based sensors where readings are periodically polled by acontroller, each sensor node 112 transmits the respective signature 200only when a stimulus is detected by the respective sensor 113.

The temporal resolution achievable by the receiver 130 is limited mainlyby a response time of the edge detection circuit, which, depending onimplementation, can be less than a few nanoseconds and be well above thesampling period of any existing sensor arrays (e.g. tactile sensorarrays). The apparatus 100 is able to resolve signatures 200 transmittedmicroseconds apart. The receiver 130 can also be configured to activatesome of its components (e.g., the filters 132) only when its edgedetection circuit detects an edge in the incoming signal. Thisconfiguration will greatly reduce the power consumption of the receiver130, particularly where the stimuli of the stimulus event are sparse.

Moreover, signal communication via the conductive fabric 111 or themesh/planar conductor portion 111′ is highly robust to damages such astears. As such, sensor nodes 112 may be flexibly arranged with respectto the conductive fabric 111 or the mesh/planar conductor portion 111′without increasing wiring complexity. Such arrangements can beconsidered to provide redundancy signal conducting paths for each sensornode 112. Therefore, density and distribution of the sensor nodes 112can be flexibly varied to suit various application requirements.

Where the communication medium 110 is implemented to include thousandsof sensor nodes 112 each associated with a unique pulse signature 200,the apparatus 100 can achieve a bit error rates (BER) of around 0.01(1%) even with the sensor nodes 112 transmitting the respective pulsesignature 200 within 1 millisecond from one another. Where the stimuliare sparse, an even lower BER is can be achieved. The apparatus 100 canachieve a high scalability, potentially up to millions of sensor nodes112.

In addition, voltage pulses are less susceptible to low frequencyinterferences (e.g. from a source of AC power noise). They can also bedetected without the need for expensive high-resolution ADCs. Voltagepulses have a much shorter duration compared to a chip in CDMA. This isequivalent to having a relatively high spread factor, achieving asignificantly higher capacity than possible with CDMA.

The pulses are bipolar and therefore the signatures 200 can beasynchronously transmitted. Conversely, Optical CDMA pulses are unipolarand thus are not decodable without the use of additional synchronizationsignals/protocols. In addition, Optical CDMA uses fibre optics, whichare not as damage resistant in terms of signal conducting path, andrequires dedicated electro-optical components.

The apparatus 100 can achieve a high scalability and can be implementedfor ultra-fast somatosensory applications. It can also maintain anear-constant ultra-high precision spatiotemporal pattern of stimulationfrom the sensors to the receiver and can support even tens of thousandsof sensors. The conductive fabric requires minimal wiring complexity,can provide high degrees of flexibility in sensor node placement, andprovides robust signal conducting paths for the sensor nodes.

With the above advantages, the apparatus 100 is particularly useful innext generation Artificial Intelligence (AI) driven-robots andautonomous systems in industries such as hospitals and home care, whererobots may be deployed in rapidly changing complex environments. It willalso be useful in many other applications involving human-machineinterfaces, such as wearable assistive exo-skeleton suits requiringrapid tactile environment feedback.

Some alternative arrangements of the present disclosures are discussedbelow.

In an alternative embodiment, the unique pulse signature of one of thesensor nodes has a first signature duration and the unique pulsesignature of another of the sensor nodes has a second signature durationdifferent from the first signature duration. That is, the unique pulsesignatures may have different numbers of pulses. The unique pulsesignatures may have different signature durations. The unique pulsesignatures may have different pulse durations. As long as the signaturesare unique, any suitable arrangements may be adopted.

In other embodiments, the sensor nodes 112 can be realised in anysuitable form of specialized analog or digital circuits.

The communication medium 110 may be adapted to cover at least a portionof, for example, a vehicle or a human.

The stimulus event may be an optical event, temperature, pressure orstimuli associated with electromagnetic waves. The stimulus event mayrelate to chemical, smell, audio, vibratory stimulation. The stimulusevent may be a combination of different stimulus types and can include2^(nd) order (processed) signals such as friction, slippage, wetness,hardness, etc. Indeed, the triggering event may be non-stimulus related.A skilled person would also appreciate that each sensor node can beassociated with any type of sensor, provided that the sensor node isassociated a signature for each possible state of detection of thesensory signal of the associated sensor.

The receiver 130 may be arranged local to the sensor nodes 112 of thereceiver 130 may be arranged remote to the sensor nodes 112 and thetransmission medium may be via any medium suitable for wirelesstransmission.

The sensors 113 may include tactile/pressure sensors of differentsensitivities. They may also include different types of sensors, such asbio-mimetic tactile receptors, optical sensors including siliconelectronics based ones, etc, acoustic sensors, piezo-electric sensorsand other sensors that may or may not have neuro-morphic features.Sensors for the detection of electro-magnetic fields, humidity, surfacetextures, vibrations, acceleration, optical, temperature, chemical,shear, proximity/light, etc., may also be included.

The conductive medium may include at least one of a conductive fabric, aconductive bulk conductor, a conductive substrate, a conductive solid, aconductive gel, and a conductive fluid, provided that the transmissionmedium is able to conduct the signatures transmitted by the sensor nodes112. The conductive fluid (e.g., conductive liquid) or the conductivegel may be in-filled within micro-channels of, for example, amicro-fluidic device.

Each sensor node 112 may be associated with additional signatures toindicate states (e.g., operation, debug, battery level, error, debug,and modalities) of the respective sensor node 112.

A variety of other variations and modifications which do not depart fromthe scope of the invention will be evident to persons of ordinary skillin the art from the disclosure herein. The following claims are intendedto cover the specific embodiments set forth herein as well as suchvariations, modifications, and equivalents.

1. A sensor-based communication apparatus comprising: a plurality ofsensor nodes associated with respective unique pulse signatures andadapted to communicate with respective sensors with each sensorconfigured to generate a sensory signal in response to a respectivestimulus, wherein each sensor node is triggered, upon receipt of thecorresponding sensory signal, to transmit the associated unique pulsesignature independently and asynchronously through a transmission mediumshared by the sensor nodes, the unique pulse signatures transmitted bythe sensor nodes being a representation of a stimulus event associatedwith the stimuli detected by the corresponding sensors.
 2. Thesensor-based communication apparatus of claim 1, wherein eachinter-pulse interval of the unique pulse signature of each of the sensornodes has a unique duration.
 3. The sensor-based communication apparatusof claim 1, wherein the unique pulse signature has eight or ten pulses.4. The sensor-based communication apparatus of claim 1, wherein theunique pulse signature of one of the sensor nodes has a first number ofpulses and the unique pulse signature of another of the sensor nodes hasa second number of pulses different from the first number.
 5. (canceled)6. The sensor-based communication apparatus of claim 1, wherein theunique pulse signature of one of the sensor nodes has a first signatureduration and the unique pulse signature of another of the sensor nodeshas a second signature duration different from the first signatureduration. 7-9. (canceled)
 10. The sensor-based communication apparatusof claim 1, further comprising tactile sensors of differentsensitivities.
 11. The sensor-based communication apparatus of claim 1,further comprising sensors including electro-magnetic, humidity, surfacetexture, vibration, acceleration, optical and/or temperature sensors.12. The sensor-based communication apparatus of claim 1, wherein eachsensor node is triggered, upon receiving a current value in thecorresponding sensory signal, to transmit a current one of theassociated unique pulse signature to indicate the current value by aninterval between the current one of the associated unique pulsesignature and a previous one of the associated unique pulse signature.13-14. (canceled)
 15. The sensor-based communication apparatus of claim1, further comprising: a receiver configured to receive through thetransmission medium an incoming signal relating to the transmittedunique pulse signatures, to correlate the associated unique pulsesignature of each sensor node with an intermediate signal relating tothe incoming signal, and to provide indication signals indicatingrespective times of triggering of the sensor nodes based on a result ofcorrelation for representation of the stimulus event.
 16. Thesensor-based communication apparatus of claim 15, wherein the receiverincludes a plurality of filters each activated, upon detection of anedge in the incoming signal by the receiver, to correlate theintermediate signal with a corresponding one of the unique pulsesignatures.
 17. The sensor-based communication apparatus of claim 1,wherein the transmission medium includes a conductive medium; andwherein the sensor nodes are distributed along the conductive medium andelectrically coupled to one another through the conductive medium. 18.(canceled)
 19. The sensor-based communication apparatus of claim 17,wherein the sensor nodes are embedded in the conductive medium. 20.(canceled)
 21. The sensor-based communication apparatus of claim 17,wherein the conductive medium is elastic and flexible.
 22. Thesensor-based communication apparatus of claim 1, wherein the conductivemedium is mesh or planar in form.
 23. The sensor-based communicationapparatus of claim 17, wherein the conductive medium includes at leastone of a conductive fabric, a conductive bulk conductor, a conductivesubstrate, a conductive solid, a conductive gel, and a conductive fluid.24. (canceled)
 25. The sensor-based communication apparatus of claim 1,wherein each sensor node is triggered, upon receipt of the correspondingsensory signal in a first state, to transmit the associated unique pulsesignature, and upon receipt of the corresponding sensory signal in asecond state, to transmit the associated further unique pulse signatureindependently through the transmission medium.
 26. The sensor-basedcommunication apparatus of claim 1, wherein each sensor node isconfigured to transmit the associated further unique pulse signatureindependently through the transmission medium to indicate an internalstate of the respective sensor node.
 27. The sensor-based communicationapparatus of claim 1, wherein the unique pulse signatures of each sensornode have different pulse polarities.
 28. The sensor-based communicationapparatus of claim 1, wherein the representation of the stimulus eventis a spatiotemporal representation.
 29. (canceled)
 30. A sensor-basedcommunication method comprising: receiving a sensory signal generated bya corresponding sensor in response to a respective stimulus, and uponreceipt of the sensory signal, triggering respective ones of a pluralityof sensor nodes to transmit an associated unique pulse signatureindependently and asynchronously through a transmission medium shared bythe sensor nodes, the unique pulse signatures transmitted by the sensornodes being a representation of a stimulus event associated with thestimuli detected by the corresponding sensors. 31-51. (canceled)